This application claims the benefit of the Korean Application No. P2000-84712 filed on Dec. 28, 2000, which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an image projector.
2. Background of the Related Art
The projector enlarges, and projects a small picture formed on a small display inside of the image projector by using a projection lens to a large sized screen, to display a large sized picture. In the image projector, there are a front projection type in which the picture is displayed on a front face of the screen, and a rear projection type in which the picture is displayed on a rear face of the screen. As a typical example of the latter, there is the projection television. As the small display in the image projector that displays the small picture, LCD (Liquid Crystal Display) and DMD (Digital Micromirror Device), and the like are employed. The LCD is provided with a polarized beam converter for displaying the picture by using a linearly polarized light.
FIG. 1 illustrates a related art image projector, FIG. 2 illustrates an operation of the polarization beam sprite array in the image projector in FIG. 1, FIGS. 3A and 3B illustrate operation of the image projector in FIG. 1, FIGS. 4A and 4B illustrate operation of the polarization beam sprite prism in the image projector in FIG. 1, and FIG. 5 illustrates a lamp with an elliptic reflector.
Referring to FIG. 1, the related art image projector is provided with a lamp 1 for emitting beams of lights, a parabolic reflector 2 for reflecting the beams to forward of the lamp 1, and a polarized beam converter for transmitting an xe2x80x98Sxe2x80x99 wave, and converting xe2x80x98Pxe2x80x99 wave into xe2x80x98Sxe2x80x99 wave and transmitting the converted xe2x80x98Sxe2x80x99 wave among the beams from the parabolic reflector 2.
The related art image projector also provided with first to third illumination lenses 10, 12, and 14 for focusing the beams polarized into a particular pole (i.e., the S wave) at the polarized beam converter, a color switch 16 for transmitting only a particular beam among the beams from the third illumination lens 14, and a polarization beam sprite prism 18 for supplying a particular color beam from the color switch 16 to a display 22, and the beam reflected at the display 22 to a projection lens 20.
The display 22 displays a picture by reflecting the color beam from the polarization beam sprite prism 18 in response to a video signal, and the projection lens 20 enlarging the beam of the picture from the display 22, and projects to a screen at a distance.
The beams of lights from the lamp 1 are incident on the polarized beam converter by the parabolic reflector 2. The polarized beam converter transmits the S wave, and converts and transmits P wave among the beams from the parabolic reflector 2. To do this, the polarized beam converter is provided with a first lens array 4, a second lens array 6, and a polarization beam sprite array 8 facing a light output surface of the second lens array 6.
The first lens array 4, or the second lens array 6 focuses the beams of light including the P wave and the S wave to a plurality of focusing points. To do this, the first, or second lens array 4, or 6 has a matrix of a plurality of lenses.
The polarization beam sprite array 8 transmits xe2x80x98Sxe2x80x99 wave, and converts the P wave into the S wave, and transmits the converted S wave, both from the second lens array 6. To do this, the polarized beam sprite array 8 is provided with polarized beam split planes 24 and reflection planes 26 both sloped with respect to the optical output surface, and half wavelength plates 28 attached to optical output surface of the polarized beam split planes 24 as shown in FIG. 2.
The polarized beam split plane 24 transmits only the P wave and reflects the S wave among the white beams from the second lens array 6. The P wave transmitted through the polarized beam split plane is converted into an S wave by the half wavelength plate 28. On the other hand, the S wave reflected at the polarized beam split plane 24 is reflected at the reflection plane 26 and forwarded as it is. That is, the entire beam of light including the P wave and the S wave passed through the polarization beam sprite array 8 is converted into the S wave.
The beam converted into the S wave at the polarized beam converter are incident on the first to third illumination lenses 10, 12, and 14 in succession. The first to third illumination lenses 10, 12, and 14 focus the beams converted into the S wave onto the color switch 16.
The color switch 16 splits red, green, and blue colors in succession so that one display cell has red, green, and blue colors in common. To do this, the color switch 16 filters a particular color beam according to a change of a voltage signal supplied from a voltage supply part (not shown). In this instance, the color beams passed through the color switch 16 are converted into the P wave from the S wave, and incident on the polarization beam sprite prism 18.
The P wave color beam from the color switch 16 to the polarization beam sprite prism 18 transmits a split plane 30 in the polarization beam sprite prism 18, and incident on the display 22.
The display 22 reflects the P wave color beam transmitted through the polarization beam sprite prism 18 according to a video signal, to produce a picture beam with picture information. In this instance, as shown in FIG. 3A, the P wave color beam reflected at the display 22 is converted into the S wave.
The picture beam converted into the S wave at the display 22 is reflected at the split plane 30 of the polarization beam sprite prism 18, and directed to the projection lens 20. To do this, the split plane 30 of the polarization beam sprite prism 18 transmits the P wave, and reflects the S wave as shown in FIGS. 4A and 4B. Accordingly, the polarization beam sprite prism 18 transmits the P wave from the color switch 16, and reflects the S wave from the display 22 toward the projection lens 20.
In the meantime, as shown in FIG. 3B, the display 22 transmits the P wave color beam from the polarization beam sprite prism 18, as it is if there is an electrical signal applied thereto. Therefore, no beam of light is directed to the projection lens 20 when the electrical signal is applied to the display 22. The projection lens 20 enlarges the picture beam from the polarization beam sprite prism 18, and projects onto a screen at a distance therefrom.
However, the color switch 16 for splitting the color beam from the beams of lights in the related art image projector has a poor light efficiency caused by poor light transmission. For compensating such a disadvantage, a color wheel may be employed in place of the color switch 16.
However, for employing the color wheel in the related art image projector, an optical system that converges the beam of light and an optical system that diverges the beam of light again are required, additionally.
Moreover, the polarized beam converter in the related art image projector requires lens arrays each having a plurality of lenses. However, the lens arrays with the plurality of lenses cause optical losses between the lenses. The number of the lenses in the lens arrays may be reduced for reducing the optical loss, but that increases a thickness of the polarization array to push the cost up. Moreover, since an optical conversion efficiency is significantly dependent on an alignment of the lens arrays, assembly of the image projector requires much time.
In addition to this, the related art image projector has the lamp with the parabolic reflector for providing parallel beams to the polarized beam converter. The lamp with the parabolic reflector has an optical efficiency poorer than a lamp with an elliptic reflector as shown in FIG. 5.
The poor optical efficiency will be explained in detail assuming that a diameter of the parabolic reflector is Dp and a diameter of the elliptic reflector is De. The lamp with the parabolic reflector directs the beam of light forward in parallel, i.e., the parabolic reflector is required to have a slope for directing the beam from the lamp forward in parallel.
On the other hand, the lamp with an elliptic reflector directs the beam of light such that the beam is focused at a plane in front of the lamp. Accordingly, the elliptic reflector is required to have a slope greater than the parabolic reflector so that the beam from the lamp is focused on the plane in front of the lamp. That is, because the lamp with the elliptic reflector can reflect more beams, the lamp with the elliptic reflector has an optical efficiency higher than the lamp with the parabolic reflector.
If the lamp with the elliptic reflector and the lamp with the parabolic reflector have the same optical efficiency, the diameter of the elliptic reflector can be made smaller than the parabolic reflector, to reduce a size of the elliptic reflector. However, since the related art polarized beam converter requires a parallel light, the lamp with the elliptic reflector can not be employed, that limits fabrication of a thinner image projector.
Accordingly, the present invention is directed to an image projector that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide an image projector which can improve an optical efficiency.
Another object of the present invention is to provide an image projector which permits fabrication of a thin image projector.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the image projector includes a lamp for emitting beams of lights, a color wheel for splitting particular color beams in succession from the beams of lights, a rod lens for making distribution of the color beams from the color wheel uniform, a polarized beam converter for converting the color beams into beams of a particular pole, an optical system for focusing the color beams converted into beams of a particular pole, a display for producing a picture beam of a video signal according to the video signal by using the color beams from the optical system, a polarization beam sprite prism between the optical system and the display for transmitting the color beams from the optical system and reflecting the picture beams from the display, and a projection lens for enlarging, and projecting the picture beams.
In another aspect of the present invention, there is provided an image projector including a lamp for emitting beams of lights, a color wheel for splitting particular color beams in succession from the beams of lights, a rod lens for making distribution of the color beams from the color wheel uniform, a polarized beam converter for converting the color beams into beams of a particular pole, an optical system for focusing the color beams converted into beams of a particular pole, a display for producing a picture beam of a video signal according to the video signal by using the color beams from the optical system, and a projection lens for enlarging, and projecting the picture beams.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.